Method of manufacturing soft magnetic dust core

Abstract

Provided is a method of manufacturing a soft magnetic dust core. The method includes: preparing coated powder including amorphous powder made of an Fe-B-Si-P-C-Cu-based alloy, an Fe-B-P-C-Cu-based alloy, an Fe-B-Si-P-Cu-based alloy, or an Fe-B-P-Cu-based alloy, with a first initial crystallization temperature T x1 and a second initial crystallization temperature T x2 ; and a coating formed on a surface of particles of the amorphous powder; applying a compacting pressure to the coated powder or a mixture of the coated powder and the amorphous powder at a temperature equal to or lower than T x1 −100 K; and heating to a maximum end-point temperature equal to or higher than T x1 −50 K and lower than T x2 with the compacting pressure being applied.

The invention claimed is: 
     
       1. A method of manufacturing a soft magnetic dust core comprising:
 preparing coated powder including amorphous powder made of an Fe-B-Si-P-C-Cu-based alloy, an Fe-B-P-C-Cu-based alloy, an Fe-B-Si-P-Cu-based alloy, or an Fe-B-P-Cu-based alloy, with a first initial crystallization temperature T x1  and a second initial crystallization temperature T x2 ; and a coating formed on a surface of particles of the amorphous powder; 
 applying a compacting pressure to the coated powder or a mixture of the coated powder and the amorphous powder at a temperature equal to or lower than T x1 −100 K; 
 heating to a maximum end-point temperature equal to or higher than T x1 −50 K and lower than T x2  with the compacting pressure being applied; and 
 thereby producing a soft magnetic dust core having a green density of 78% or more, a crystallization degree of 40% or more, and α-Fe crystallites with a size of 50 nm or less. 
 
     
     
       2. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein the amorphous powder has a composition containing, in atomic percent:
 Fe: 79% or more and 86% or less; 
 B: 4% or more and 13% or less; 
 Si: 0% or more and 8% or less; 
 P: 1% or more and 14% or less; 
 C: 0% or more and 5% or less; 
 Cu: 0.4% or more and 1.4% or less; and 
 incidental impurities. 
 
     
     
       3. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein the composition contains total 3 at. % or less of at least one selected from the group consisting of Co, Ni, Ca, Mg, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, Y, N, O, S, and rare earth elements, instead of part of Fe. 
     
     
       4. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein a mean particle diameter D 50  of the amorphous powder is 1 μm to 100 μm. 
     
     
       5. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein a mean particle diameter D 50  of the amorphous powder is 1 μm to 100 μm. 
     
     
       6. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein an apparent density AD (Mg/m 3 ) of the amorphous powder and the mean particle diameter D 50  (μm) satisfy AD≥2.8+0.005×D 50 . 
     
     
       7. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein an apparent density AD (Mg/m 3 ) of the amorphous powder and the mean particle diameter D 50  (μm) satisfy AD≥2.8+0.005×D 50 . 
     
     
       8. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein a crystallization degree of the amorphous powder is 20% or less. 
     
     
       9. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein a crystallization degree of the amorphous powder is 20% or less. 
     
     
       10. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein crystalline soft magnetic powder is mixed with the amorphous powder or the coated powder. 
     
     
       11. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein crystalline soft magnetic powder is mixed with the amorphous powder or the coated powder. 
     
     
       12. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein the compacting pressure is 100 MPa to 2000 MPa, and
 a holding time is 120 minutes or less, the holding time being defined as a time after the heating to the maximum end-point temperature, during which the maximum end-point temperature is kept while the compacting pressure is applied. 
 
     
     
       13. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein the compacting pressure is 100 MPa to 2000 MPa, and
 a holding time is 120 minutes or less, the holding time being defined as a time after the heating to the maximum end-point temperature, during which the maximum end-point temperature is kept while the compacting pressure is applied. 
 
     
     
       14. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein the heating is performed by electrical heating. 
     
     
       15. The method of manufacturing a soft magnetic dust core, according to  claim 2 , wherein the heating is performed by electrical heating. 
     
     
       16. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein the heating is performed using at least one heating source placed inside, outside, or both inside and outside a mold used for the application of the compacting pressure. 
     
     
       17. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein the heating is performed by both
 electrical heating, and 
 heating using at least one heating source placed inside, outside, or both inside and outside a mold used for the application of the compacting pressure. 
 
     
     
       18. The method of manufacturing a soft magnetic dust core, according to  claim 1 , wherein prior to the application of the compacting pressure, the amorphous powder is preformed at a filling rate of 70% or less.